Bypass ratio is defined as the ratio of mass airflow through the fan section to the mass airflow that passes through which portion of the engine?

• A. Gas generator portion
• B. Combustion chamber
• C. Turbine section
• D. Intake plenum

Answer: (A)

Bypass ratio compares how much air the fan moves with how much air actually goes through the engine’s core. The denominator is the mass flow through the gas generator portion—the core path that includes the compressor, combustor, and turbine. This is the part of the engine where fuel is burned and power is produced, so it represents the core air flow that the bypass air is being compared to. The other options are just individual components or the entry path: the combustion chamber and turbine are part of the core, but not the entire core flow by themselves; the intake plenum is simply the air intake before the core. Hence, the ratio uses fan air divided by core air flowing through the gas generator portion.